"There will be the usual competition stuff - a march, a concert programme, a hymn and a test piece."
The championships were being held at the Memorial Theatre in the South Taranaki town.
Attention then turns to preparing for Last Night of the Prom for the first time since 2014.
A big production with "lots of fanfare" is set for November 5 at the Royal Whanganui Opera House.
"There will be traditional proms music, but also a lot of new ideas around that as well," Jellyman said.
"The people who set up proms (promenades) originally in England, like Sir Henry Wood, their aim was not to play such heavy orchestral music.
"It was lighter and more approachable, which fits our whole thing."
The first season of proms concerts opened at Queen's Hall in London in 1895, as a way to allow commoners to attend concerts.
In French, "se promener" means "to walk", with the founding idea being that people could have standing places at a minimal cost.
The show in November will also feature vocalists Jennifer Little and Jamie Henare, and a prom choir.
Three members of the A-grade band - Luke Squire, Toby Clark and Bryn Morgan - had been selected for the national secondary schools brass band, Jellyman said.
All three attend Whanganui High School.
They will head to a training camp in Christchurch from October 5 to 8 to work with musical directors Andrew Snell and Reuben Brown.
"That really is a huge achievement. They have to audition for it, and now they get to go on tour," Jellyman said.
Tickets for Last Night of the Proms go on sale on August 5.
